This invention relates to a cushioned railway trailer hitch or stanchion, and more specifically to such a hitch in which an elastomeric material in compression is utilized to cushion impact loading between a trailer carried by the railway car and the railway car upon movement of the car in longitudinal direction along the track, and particularly upon abrupt longitudinal accelerations of the car, such as during humping or other switch yard operations.
Generally, it is common for over-the-road trailers to be loaded onto a specially designed railway flat car which accommodates one or more (typically, two) such trailers. This type of railway service is often referred to as intermodal or piggyback service. In such intermodal service, the wheels of an over-the-road trailer support the rear of the trailer on the railway car and the car is provided with a hitch which supports the front of the trailer. Typically, the hitch includes a hitch head which is positioned generally at the height and functions generally the same as a "fifth wheel" on an over-the-road tractor. The trailer has a downwardly extending kingpin on the front of the trailer which is engaged by the hitch head, with the latter capturing the trailer kingpin. Typically, the hitch head includes a locking assembly which is the sole means for securing the trailer to the railway car. Consequently, the hitch must not only securely hold the front of the trailer on the railway car, but the hitch must withstand and resist all inertial or acceleration loads between the railway car and the trailer.
In humping or other switch yard operations, substantial amounts of energy must be transmitted through the hitch between the railway car and the trailer. For example, in a ten-mile per hour impact of the railway car, which may represent a severe impact during actual humping operations or the like, such an impact force requires that the maximum force applied to the trailer kingpin must be limited, in accordance with the Association of American Railroads (AAR) standards so as not to exceed a force of 210,000 pounds. In an effort to minimize such kingpin loading during railway operation, cushioned hitches have been developed. Reference may be made to such U.S. patents as follows for examples of such cushioned hitch arrangements: U.S. Pat. Nos. 3,145,006, 3,246,866, 3,493,207, 3,512,739, 4,095,766, and 4,095,767.
A hitch typically includes a vertical strut and a diagonal strut, both of which are pivotally secured to the railway car. The hitch head is normally pivotally carried on the upper end of the vertical strut. The diagonal strut is typically pivotally secured to the upper end of the vertical strut proximate the hitch head. Certain prior art hitches are movable between a raised or erected position for supporting the forward end of an over-the-road trailer, and a lowered or retracted position in which the hitch is folded onto the floor of the railway car so that a tractor and the trailer may be driven lengthwise onto and from the railway car. In other prior art hitches, the hitch remains erect in its operating position, and the over-the-road trailers are lifted onto and from the car.
In any event, whether the hitch is retractable or is fixed in erected position, the vertical strut of the hitch predominantly supports the weight of the trailer and withstands virtually all of the vertical loads imposed on the hitch during operation. The diagonal strut supports the vertical strut and the hitch in longitudinal (i.e., fore and aft direction with respect to the car) and must withstand substantially all of the longitudinal inertial loads between the railway car and the trailer. In cushioned hitches, an energy dissipating or cushioning system is typically incorporated within the diagonal strut. However, such energy dissipating or cushioning systems may, as shown in U.S. Pat. No. 3,493,207, be incorporated in the hitch base. In any event, these cushioning systems must, in a ten-mile per hour impact, dissipate about 85,000-90,000 foot pounds of energy so as to prevent the load applied to the kingpin of the trailer from exceeding the above-noted 210,000-pound maximum kingpin load limit, as established by AAR regulations.
Generally, two types of cushioning systems for such railway hitches are in general use, namely a hydraulic cushioning unit or an elastomeric unit. Hydraulic cushioning units, such as shown in the co-assigned U.S. Pat. Nos. 3,246,866 and 3,512,739, utilize a hydraulic cylinder filled with a hydraulic fluid or liquid which, upon being subjected to elongation or compression forces, was metered through an appropriate metering orifice, thus dissipating energy and cushioning the trailer against impact loads. While these and other hydraulic cushioning units worked well for their intended purposes, by their nature, they required many machined parts and close tolerances in the hydraulic portion of the cushioning unit. These high tolerance and complex machined surfaces required significant amounts of cost and manpower for fabrication, inspection, and maintenance purposes. Additionally, since hydraulic cushioning units work primarily on the principle of dissipating the momentum of the railway car or trailer through a change in the momentum of the hydraulic fluid within the cushioning unit, the cushioning capability of such hydraulic cushioning units is dependent on the characteristics of the hydraulic fluid. Moreover, for a hydraulic cushioning unit, the force applied to the kingpin of a trailer is a function of the velocity of the hydraulic cushioning unit deflection, and this is a complex functional relationship between a variety of parameters which can result in a different curve of velocity versus strut deflection to be produced for each impact initiation speed.
Reference may also be made to U.S. Pat. Nos. 3,145,006, 3,493,207, 4,905,766, and 4,095,767, which show a compendium of prior art elastomeric cushioning units. More specifically, in U.S. Pat. No. 3,145,006, a trailer hitch is shown in which a rubber in compression energy absorption unit is incorporated in the diagonal strut so as to resist both inward and outward movement thereof. The elastomeric or resilient energy absorption system shown in this last-noted patent is not described in detail, but it is evident from the drawings it is of a construction and method substantially different from that disclosed and claimed herein.
U.S. Pat. No. 3,493,207 discloses a foldable hitch arrangement which, as shown in FIG. 16, utilizes a number of superposed resilient elastomeric pads which are bonded to the adjacent faces of metallic separating plates with a suitable adhesive. These elastomeric members are stressed in shear rather than in compression. (See column 9, lines 29 et seq of U.S. Pat. No. 3,493,207.)
The co-assigned U.S. Pat. Nos. 4,095,766 and 4,095,767 disclose other types of elastomer-in-shear cushioning units incorporated within the diagonal struts of a hitch. Many various structural arrangements of the elastomer-in-shear and elastomeric energy absorption elements are illustrated in these patents.
However, as can be appreciated in all types of elastomer-in-shear constructions, the energy absorbing characteristics are dependent on the adhesive bond between the elastomeric units and its corresponding shear backing plates. In service, over time, the elastomer-in-shear cushioning units are exposed to the elements, large temperature extremes, and a large variety of solvents and other fluids which tend to weaken the bond between the elastomer members and their backing plates.
It is also known to utilize elastomer-in-compression for energy absorption purposes. For example, in U.S. Pat. No. 3,751,020, assigned to Miner Enterprises, Inc., of Chicago, Ill., a shock absorber is disclosed in which a piston assembly is movable in a chamber to the extent of an air space provided in unresisted fashion by a compressible solid during short strokes of a piston rod, but is resisted by the compressible elastomer solid during long strokes of the piston rod.
In U.S. Pat. No. 4,198,037, also assigned to Miner Enterprises, Inc., an elastomeric compression spring is shown in which a plurality of elastomeric blocks of an annealed copolyester polymer elastomer are bonded to the respective sides of metallic plates interposed therebetween so that upon application of a compression load, the elastomeric members will deform along their peripheral edges. Here again, however, the structural integrity of the elastomeric cushioning unit is dependent on a bonded joint between the elastomeric member and the metal plate adhesively bonded thereto.
There has been a long-standing need for a trailer hitch cushioning apparatus which would be substantially unaffected during a long service life, which would dissipate substantial amounts of energy, and which was not dependent on close tolerance hydraulic parts or on an adhesive joint.